In textile industry, a key factor to maintain consistent quality of fabrics produced by each flat bed knitting machine is controlling the size of stitches knitted through yarns. The size of the stitches is formed by the amount of the yarns latched by needles. When there is a need to produce a great amount of one type of fabrics, the stitch formed by each flat bed knitting machine must be controlled at the same size whenever possible. In the event that the stitches of fabrics produced by different flat bed knitting machines are different, the cams driving the needles to perform yarn latching operation have to be adjusted. However, the size of the stitches is difficult to differentiate by people's naked eyes. Hence scientific measuring devices are needed to perform the task. Namely, by measuring yarn utilization during operation of the flat bed knitting machines, the stitch differences among the flat bed knitting machines can be compared and determined. Then the up and down positions of the cams of the flat bed knitting machines can be adjusted to stabilize fabric quality.
One of references to meet the purpose set forth above is U.S. Pat. No. 6,112,557 entitled “Flat bed yarn measuring device and method”. Referring to FIGS. 1, 2 and 3 of that patent, the device adopts a technique in which a yarn 17 first drives a wheel 19 rotating when the flat bed knitting machine is operating. An electrically connected logic circuit control box 21 is provided to receive rotational signals generated by the wheel 19. There is a sensor 24 located on a carriage 10 above needle beds 13 and 14 that is movable on a track 15; and movement thereof can be detected by a home magnet 26, a first magnet 27 and a second magnet 28 that are fixedly mounted onto a stationary bar 25 and spaced from one another at a selected distance to generate respectively a reset signal, a start signal and a stop signal. These signals are received by the logic circuit control box 21 through the electrically connected sensor 24, so that the logic circuit control box 21 is reset to zero, and a statistical start point and a statistical stop point of the rotational signals generated by the wheel 19 can be controlled. For instance, given a 12 cut flat bed knitting machine, namely there are 12 needles for each inch on the flat bed knitting machine, to allocate 100 needles at a selected distance about 8.33 inches (or 21.1 cm for the metric system) is needed between the first magnet 27 and the second magnet 28, and the home magnet 26 is located outside the selected distance close to the first magnet 27. When the flat bed knitting machine starts operation, the carriage 10 first drives the sensor 24 to the home magnet 26 to be detected and reset to zero. Meanwhile, the yarn 17 drives in advance the wheel 19 to generate a rotational signal sent to the logic circuit control box 21. But the logic circuit control box 21 dose not start receiving and counting the rotational signal. When the carriage 10 continuously moves close to the first magnet 27, the sensor 24 detects and generates a signal to the logic circuit control box 21, then the logic circuit control box 21 starts receiving and accumulating the rotational signal generated by the wheel 19. When the carriage 10 continuously moves to the second magnet 28 for the selected needle distance (about 21.1 cm for 100 needles), the sensor 24 detects again and generates another signal to the logic circuit control box 21, and the logic circuit control box 21 stops receiving and accumulating the rotational signal generated by the wheel 19. Then the machine can be stopped to see a display 42 of the logic circuit control box 21. The logic circuit control box 21, through the radius (r) derived by the distance between the preset center of the wheel 19 and the contact circumference of the yarn 17, or a circumferential length entered in advance (through equation: L=2πr, circumference index π=3.1416) and accumulating received amount of the rotational signal of the wheel 19, total used amount of the yarn 17 at the selected distance of the needles (i.e. 100 needles) can be calculated (i.e. circumferential length×accumulating received amount through the rotational signal). Or yarn consumption of each needle can be obtained by dividing with 100. Hence the size of the stitch can be compared and determined. Thereby the up and down movement of the cams can be adjusted.
However, the conventional yarn measuring device mentioned above still has drawbacks in practice, notably:
1. The conventional yarn measuring device previously discussed can measure only in one direction. The home magnet 26 has to be reset to zero before starting receiving the rotational signal. Based on technical perspective, removing the home magnet 26 or adding another home magnet 26 close to the second magnet 28 still cannot easily perform bidirectional measurement. Without the home magnet 26 resetting to zero, the logic circuit control box 21 will do accumulation endlessly, and a desired measured value cannot be calculated and obtained. But adding the home magnet 26 beyond two ends of the first magnet 27 and second magnet 28, after the sensor 24 has detected the first magnet 27 and the logic circuit control box 21 starts accumulation, and at the instant the sensor 24 also detects the second magnet 28 and accumulation is stopped, the logic circuit control box 21 is reset to zero by the home magnet 26 close to the second magnet 28 before process is started. Hence the process is suspended. As a result, the measuring device has to reset the home magnet 26 to zero before performing each measurement. This one way measurement causes many disadvantages. For instance, the cam on the carriage to drive the needles in the forward movement is different from the one in the backward movement. As the cams have allowances during fabrication, and tolerances also exist during assembly, measurement of yarn consumption during the forward movement can be obtained to adjust the cam, but measurement of the backward movement can not be obtained and adjustment of the cam cannot be done. As a result, different sizes of fabric stitches will be formed.
2. The error range of the measured value of the conventional yarn measuring device is too great. Due to the yarn 17 is fed constantly during operation of the flat bed knitting machine, friction occurs between the circumferential surface of the wheel 19 and the yarn 17, and the yarn 17 drives the wheel 19 rotating. As previously discussed, the yarn consumption can be measured by the rotational times of the wheel 19, the error range of the measure value depends on the circumferential length of frictional contact between the wheel 19 and the yarn 17, or the radius that determines the circumferential length of the wheel 19. As the length of frictional contact between the yarn 17 and the circumference of the wheel 19 is not sufficient, sliding could occur and driving of the wheel 19 could be not possible. In such an occasion, the measured value has little meaning. To prevent such a phenomenon from occurring, the length of frictional contact between the yarn 17 and the circumference of the wheel 19 has to be increased, namely the circumference or radius of the wheel 19 has to be greater. But increasing the circumference of the wheel 19 also makes the error range of the measured value greater. As measurement of yarn consumption is calculated by the rotational times of the wheel 19, when the wheel 19 rotates close to one time but not exactly one time, an error occurs to the measured yarn consumption at that time. In the conventional technique, no matter how much the circumference of the wheel is reduced, the error range of the measured value still is too large. For instance, given a minimum wheel radius of 0.25 cm as a reasonable and practical value, the circumferential length is about 1.57 cm, and the measured value error range is about 0 to 1.56 cm. Namely the maximum error value is about 1.56 cm. With the error value at such a size, the accuracy is not desirable.
3. Reading of the measured value of the conventional yarn measuring device is difficult. As the logic circuit control box 21 is located on the carriage 10, and the display 42 is located on the logic circuit control box 21, reading the process result displayed on the display 42 has to be waited until the carriage 10 has finished moving. It is inconvenient for users.
4. Adjustment of the cams on the conventional yarn measuring device is tedious. As reading of the process result on the logic circuit control box 21 can be done only after the carriage 10 has stopped moving, then the cams can be adjusted in a still manner. After adjustment, the process result can only be obtained by reading the logic circuit control box 21 after the carriage 10 has stopped moving again, then another adjustment of the cams can be made. It is a tedious operation. Such a device that does not allow the process result to be directly read while the carriage is moving and the cams to be adjusted quickly and dynamically cannot meet the present market requirement.